Tuned transformer



' April 3, 1928. '1,664,541

G. H. COOPER TUNED TRANSFORMER Filed Aug. 5. 1927 Patented Apr. 3, 1928.

GEORGE H. COOPER, OF HARTFORD, CONNECTICUT.

y TUNED TRANSFORMER.

Application filed August 3, 1927. Serial No. 210,354.

This invention relates to those transformers which are provided foramplifying electric signal waves such, for instance, as are used inradio receiving sets. In order to obtain the desired effect it is commonpractice to wind the coils of the transformers with an approximatenumber of turns of wire and test to note the result and ythen add orsubtract turns of wire until the required condition is obtained, or toplace a fixed capacity or adjustable capacity across, and electricallyconnected with, one or both windings. This in commercial quantityproduction requires skill, consumes valuable time and adds expense.

The present conception provides a very simple method of making andtuning such transformers whereby they may be rapidly produced in largenumbers and will be accurately and uniformly tuned and remain in thedesired condition. A further advantage also is that the method of tuningaccording t0 this invention is so 'simple that it can be practiced byrelatively unskilled persons.

This is attained by winding a definite pre'- determined number of turnsof wire upon a spoolof vinsulation that has no metallic core, whichturns are always the same and remain the same for transformers of thelike frequency, and which will produce a slightly higher frequency thanthat ultimately de-` sired. The structure is then tuned down byinsertingone or more' Very small strips of iron in an opening in thecenter of the spool to compensate for variations of inductance in'thewindings and distributivev capacity' of the windings and their support.This element thus tuned is placedl in an insulating case and after thewire terminals are attached .to contact pins, or' suitable terminaldevices, it is further tuned by folding one or .more very small stripsof iron over the end and down the sides of the s 001. When finally tuneda cover is applic to the case and sealed air tight.

Fig. 1 ofthe acom anying drawings shows a side elevation of thetransformer with the case c ut in section. Fi 2 shows a plan with thecover removed. 1g. 3 shows a section of the spool and coils. Fig. 4shows on greatly enlarged scale one of the iron tuning strips that maybe applied over the end and down the sides of the spool. Fig. 5.shows aniron tuning strip which may be inserted in the center of the spool.

The spool of the transformer illustrated is made of wood or othernonmetallic insulating composition, with a flange 1 at the top, a flange2 at the bottom, and an intermediate iiangc 3 nearer thiI lower end thanthe upper end. The spool has a central bore 4. The primary wire 5 iswound in the narrow lower space of the .spool and the secondary -6 iswound in the wide upper space of the spool. n

In the manufacture of these transformers the wire, preferably singlesilk enamel wire, is wound on the spool with a definite predeterminednumber of turns, vand that number of turns is adhered to for alltransformers of the same frequency. In practice the number of turns issuch as to produce a slightly higher ircquency than is ultimatelydesired. The element thus produced is then tuned down tn a desiredfrequency by inserting into the central bore of the spool one or morethin narrow strips of iron 7 which will compensate for any variation offrequency resulting from the windings. The strip of strips placed in thebore and which preferably extend the full length of the spool may beretained in placeby a drop of wax 8. This element is then fastened in acase 9, preferably cylindrical, of insulating material, and the wireterminals connected with the contact terminals 1() that extend throughthe case. When the element thus tuned to compensate for variations inthe windings and spool capacity is in the case one or more thinnarrow-strips of iron 11 bent to extend over the end and down the sidesmay be applied to the spool. A strip of paper 12 is preferably placedunder this exterior strip to insure insulation. Drops of wax 13 may beused to hold the ends o this strip in fixed position. This exteriorstrip bent over the end and down the sides of the spool further tunesthe element and may be applied after the element is inserted in the caseso as to take care of anfy irregularity incident to capacity effect othe case or the retaining wax. The exterior strip also tends to shieldthe windings from outside interference. The strip may, if desired, beomitted from the bore, but if vomitted the element cannot be tuned ascritically as by its use.

loo

After the activ element has been placed in v the case a cover 14 issealed u on the top so that the closure will be air tig t.

With the construction illustrated there is no substantial iron core toabsorb ener and create disturbing yiuluens. The simple tuning strips,which are very inexpensive,

, can be quiclriy applied or removed to obtain the desired frequencyWithout disturbing the windings which once made need not loe altered.This in commercial quantity manufacture is oi great advantage. By makingand tuning the transformers in the manner above described large numberscan be turned out so that they will be uniform and will accurately keeptuned to the frequency for which they are rated, although of course, themethod of tuning set forth may be made use of by relatively unskilledpersons build-vr ing transformers in small quantities.

The invent-ion claimed is:

l. rllhe method of producing a tuned transormer which consists inWinding' primary and secondary coils of predetermined deii nite numbersoi? turns upon a. spool of insulation and tuning the same by folding athin narrow strip or strips of iron over the end and down the sides ofsaid spool.

2. The method of producir-ig a tuned transl former which consists inWinding primary and secondary coils ofi predetermined denite numbers ofturns upon a spool of insulation and tuning the same by inserting athin,y

` GERGE H. CQPER.

#EERTMQATE @il SRREGHN.

raam ne.. sai.

Granted April 14.3.12??g te seeker a. eeerer..

lt 'ie hereby eeriiie tha error appears iii the printed specificatie@ of@be above numbered paient requriagg corre-mien for thepwor fpreduee"read "rede-ee" be read with this eerreetien therein the ease in thePatent i'iee.,

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(Seal) E M. 3. Moore., Acting Commissioner of Patents.

